You must be at least 21 years old to enter a casino and gamble in most states in the United States. This age requirement is strictly enforced to prevent minors from participating in gambling activities. Casinos typically check identification to verify the age of patrons before allowing them to enter the gaming areas. It is important to adhere to age restrictions and regulations when visiting a casino to avoid any legal consequences. Always carry a valid form of identification to prove your age if requested by casino staff.